Former city Public Advocate Mark Green on Tuesday ditched Gov. Cuomo and endorsed his rival, Zephyr Teachout, in next week’s Democratic primary.

Green becomes the most prominent Democrat to endorse the lefty Fordham Law professor’s underdog campaign.

Green criticized Cuomo for meddling with his commission to combat public corruption and for refusing to debate Teachout.

“While the governor surely has accomplishments, I held him up to his own high standards of openness, progressiveness, reform . . .” said Green. “I had hoped for a governor more principled than political, more candid than transactional, more progressive than hair-splitting.”

Green noted that Teachout and running mate Tim Wu lack experience in politics and government service. “But,” he added, “there are times when experience takes a back seat to the kind of fresh idealism that can truly shake up politics-as-usual in Albany. ”

Green lost to Cuomo in the 2006 race for state attorney general.

Cuomo argued that debates don’t always serve voters well. “I’ve been in many debates that I think were a disservice to democracy — so anyone who says debates are always a service to democracy hasn’t watched all the debates that I’ve been in.”